Axially Articulated and Rotationally Locked Backup Ring Assembly for a Sealing Element

ABSTRACT

A backup or extrusion barrier ring assembly has multiple rows of rings in segments that have circumferentially offset slots. The rings are rotationally locked to each other to maintain the circumferential offset of the slots that allow the rings to be more flexible in the setting process. The rings as a unit can be mounted to relatively rotate on a supporting mandrel. The rings are mounted to allow them to move axially during setting either in tandem or axially relatively to each other. The axial run in heights of rings decline from innermost to outermost so that when set the heights approach each other to minimize or eliminate sharp ends against the seal. Alternatively, the height difference can be such as to allow ends to bend over an adjacent end further out radially so that free ends bend toward the surrounding tubular and avoid the seal.

FIELD OF THE INVENTION

The field of the invention is sealing systems for subterranean tools against tubular or open hole or cased hole and more particularly anti-extrusion barriers for low, medium and extended reach for a seal element.

BACKGROUND OF THE INVENTION

In the unconventional drilling and completion industry, oil and gas deposits are often produced from tight reservoir formations through the use of fracturing and frack packing methods. To frack a well involves the high pressure and high velocity introduction of water and particulate media, typically a sand or proppant, into the near wellbore to create flow paths or conduits for the trapped deposits to flow to surface, the sand or proppant holding the earthen conduits open. Often, wells have multiples of these production zones. Within each production zone it is often desirable to have multiple frack zones. For these operations, it is necessary to provide a seal known as a frack packer, between the outer surface of a tubular string and the surrounding casing or borehole wall, below the zone being fractured, to prevent the pumped fluid and proppant from travelling further down the borehole into other production zones. Therefore, there is a need for multiple packers to provide isolation both above and below the multiple frack zones.

A packer typically consists of a cylindrical elastomeric element that is compressed axially, or set, from one end or both by gages within a backup system that cause the elastomer to expand radially and form a seal in the annular space. Gages are compressed axially with various setting mechanisms, including mechanical tools from surface, hydraulic pistons, atmospheric chambers, etc. Setting typically requires a fixed end for the gages to push against. These fixed ends are often permanent features of a mandrel but can include a dynamic backup system. When compressed, the elastomeric seal has a tendency to extrude past the gages. Therefore, anti-extrusion backups have become common in the art. However, typical elastomeric seals maintain the tendency to extrude through even the smallest gaps in an anti-extrusion backup system.

In cased-hole applications, anchoring of compression set packers is a common feature in the completion architecture. Anchoring is provided by wedge-shaped slips with teeth that ride up ramps or cones and bite into the casing before a packer is set. These systems are not part of the backup system nor are they designed to provide anti-extrusion. Often they are used in the setting of the packer to center the assembly which lowers the amount of axial force needed to fully set the elastomer seal. Once set, anchoring systems are also useful for the life of the packer to provide a uniform extrusion gap, maintain location and help support the weight of a bottom-hole assembly in the case of coiled tubing frack jobs. Anchors also prevent tube movement in jointed strings resulting from the cooling of the string by the frack fluid. Movement of the packers can cause them to leak and lose seal.

In open-hole frack pack applications it is rarer for the packer to have anchoring mechanisms, as the anchor teeth create point load locations that can overstress the formation, causing localized flow paths around the packer through the near well-bore. However, without anchors, movement from the base pipe tubing can further energize the elastomeric seal. Energizing the seal from tube movement tends to overstress the near wellbore as well, leading to additional overstressing of the wellbore, allowing communication around the packer, loss of production, and potential loss of well control to surface. However, the art of anchoring has been reintroduced in new reservoirs in deep-water open-hole fracking operations. The current state of the art in open-hole frack pack operations requires a choice between losing sealing due to anchor contact induced fractures, packer movement, or over-energizing of the elastomeric element.

Extrusion barriers involving tapers to urge their movement to block an extrusion path for a sealing element have been in use for a long time as evidenced by U.S. Pat. No. 4,204,690. Some designs have employed tapered surfaces to urge the anti-extrusion ring into position by wedging them outwardly as in U.S. Pat. No. 6,598,672 or in some cases inwardly as in U.S. Pat. No. 8,701,787. Other designs simply wrap thin metal rings at the extremities of the sealing element that are designed to contact the surrounding tubular to create the anti-extrusion barrier. Some examples of these designs are U.S. Pat. No. 8,479,809; U.S. Pat. No. 7,708,080; US 2012/0018143 and US 2013/0147120. Of more general interest in the area of extrusion barriers are U.S. Pat. No. 9,140,094 and WO 2013/128222.

In some applications the gap across which the seal is expected to function is quite large placing such applications beyond the limits of the design in U.S. Pat. No. 6,598,672.

The present invention addresses operational issues in the past with a multi-layer ring assembly of nested rings with circumferentially offset slots where the ring heights decline from the innermost to the outermost rings in the assembly. The rings are rotationally locked to each other to maintain the slot circumferential offset. The nested ring assembly is mounted for axial relative articulation during the set so that the number of sharp edges exposed to the sealing element is reduced if not eliminated. The free ends of rings inside the outermost ring can be bent by the sealing element during the setting in a way to protect the sealing element from sharp ends as the ends of the rings are protected by an adjacent ring and the innermost ring is bent toward the surrounding tubular to shield sharp ends of the rings further out from contact with an end of the sealing element. These and other aspects of the present invention will be more readily understood from a review of the description of the preferred embodiments while recognizing that the full scope of the invention is to be determined by the appended claims.

SUMMARY OF THE INVENTION

A backup or extrusion barrier ring assembly has multiple rows of rings in segments that have circumferentially offset slots. The rings are rotationally locked to each other to maintain the circumferential offset of the slots that allow the rings to be more flexible in the setting process. The rings as a unit can be mounted to relatively rotate on a supporting mandrel. The rings are mounted to allow them to move axially during setting either in tandem or axially relatively to each other. The axial run in heights of rings decline from innermost to outermost so that when set the heights approach each other to minimize or eliminate sharp ends against the seal. Alternatively, the height difference can be such as to allow ends to bend over an adjacent end further out radially so that free ends bend toward the surrounding tubular and avoid the seal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a section view showing a stack of three rings with different axial lengths;

FIG. 2 is a top view of a segment that makes up a ring in FIG. 1 showing a slot that allows axial movement and rotational locking to at least the other ring segments in the assembly;

FIG. 3 is the set position of FIG. 1;

FIG. 4 is a rolled flat top view of a ring segment showing slots at one end and wider slots at an opposite end for segment mounting;

FIG. 5 is a section view of rings with different lengths where at least one ring has an end bend when running in;

FIG. 6 is a section view near the ends of stacked ring segments showing reduced height from innermost to outermost rings;

FIG. 7 shows the ends of FIG. 6 in the set position against a surrounding tubular;

FIG. 8 is the set position of the rings shown in FIG. 5;

FIG. 9 is a section view of set rings that were the same height at run in;

FIG. 10 is a section view when running in of rings of differing lengths;

FIG. 11 is the view of FIG. 10 in the set position with the ends extending substantially the same axial height;

FIG. 12 is an end view of a portion of radially stacked rings with their gaps at the smallest during running in;

FIG. 13 is the view of FIG. 12 with the offset gaps between layers enlarged in the set position with extrusion paths still prevented.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 shows a part of a borehole packer that is mounted on a mandrel 10 and further illustrates the run in position of the sealing element 12 at one end. Those skilled in the art will recognize that the opposite end of the sealing element 12 has a mirror image layout of the parts that will now be described. Rings 14, 16 and 18 are nested to each other and supported by mandrel 10. Each of rings 14, 16 and 18 are preferably in segments with a segment shown rolled flat in FIG. 4. Narrow slots 20 start from end 22 and wider keyways 24 start from opposite end 26 for ease of assembly. Alternatively, keyways 24 can be elongated openings that come short of end 26. Referring back to FIG. 1 ring 28 is supported from mandrel 10 either fixedly or with a bushing or bearing that permits ring 28 to rotate relatively to mandrel 10. Mounting ring 30 is threaded to ring 28 and features threaded openings 32 that accept a threaded rod or stud that can go through the keyways 24 of rings 14, 16 and 18 to prevent relative rotation among rings 14, 16 and 18. Although each of the rings 14, 16 and 18 are preferably made of abutting segments one of which is shown in FIG. 4, those skilled in the art will appreciate that rotationally locking one of several segments that make up a ring locks the entire ring against rotation relative to other rings through which the stud 34 extends. The abutting segments can be attached at run in and can release from each other in the set position. The need to avoid relative rotation among rings 14, 16 and 18 is best understood from FIGS. 12 and 13. In FIG. 12, gaps 20 are offset among rings 14, 16 and 18 in the run in position with the gaps 20 having their narrowest circumferential dimension. That circumferential dimension grows as shown in FIG. 13 when the set position is obtained. However, because there has been no relative rotation among rings 14, 16 and 18 during the set the now broader gaps 20 are still covered as between adjacent rings 14, 16 and 18 so there are no extrusion gaps. While all the rings 14, 16 and 18 can rotate relatively to the mandrel 10 to preserve the movements of FIG. 12 to FIG. 13, the individual rings should not rotate with respect to each other to avoid creating extrusion paths in the set position of the sealing element 12. Allowing relative rotation of the rings 14, 16 and 18 relative to mandrel 10 can also ensure better contact with the surrounding tubular whose wall can have surface irregularities that would otherwise snag the rings 14, 16 and 18 as they are pushed out to the surrounding tubular during the setting process.

Returning to FIGS. 1 and 2 the keyways 24 permit axial movement of either all the rings 14, 16 and 18 together or relative movement in the axial direction as between or among rings 14, 16 and 18. Although three rings 14, 16 and 18 are discussed, those skilled in the art will appreciate that other quantities of such nested rings can be used. Some of the openings 32 can accommodate a stud 34 that instead of extending through aligned keyways 24 of rings 14, 16 and 18 can actually bear on the outermost ring 14 at a circumferentially offset location from the location of keyways 24 so that the rings 14, 16 and 18 are in effect pushed together to control the friction force between or among them and with that regulate their tendency to move relatively to each other in the axial direction during the setting process.

As shown in FIGS. 1 and 6 the axially longest ring 18 is the innermost ring and the next two adjacent rings 16 and 14 going in a radially outward direction are axially shorter. If the axial length of the rings in the run in position was the same, their end profile in the set position would look like FIG. 9 where sharp edges 36, 38 and 40 would present themselves facing the element 12 and dig into it potentially causing pieces to be cut off at opposed ends of the element 12. Using differing heights such as illustrated in FIGS. 1 and 6 when the set position is attained can reduce the number of sharp edges acting on the sealing element 12 to a single edge such as 40 in FIG. 7 on ring 18 while similar edges on rings 16 and 14 are protected from sharp edges contacting the sealing element 12 and instead present blunt ends to the end of the sealing element 12. Taking the use of height differences among rings in the run in position one step further, FIGS. 10 and 11 show that with the right height differences among the rings 14, 16 and 18 for run in, their relative heights can be close to the same in the set position as shown in FIG. 11 so that what is in essence a blunt surface 46 is presented against the sealing element 12. The innermost ring 18 could still potentially form an edge 48 against the sealing element 12 in the set position but that edge can be rounded off in manufacturing to minimize the impact on the sealing element 12 even in the FIG. 11 configuration with the blunt edge 46.

As shown in FIG. 3 with the right axial height differences and with an initial parallel end configuration of the rings 14, 16 and 18, the setting can result in the outermost ring 14 sitting flush against the surrounding tubular 50 while end 52 bends over the end of outermost ring 14 and end 54 of ring 18 bends over the bend 52 of ring 16. In this way the ring ends 52 and 54 are oriented toward the tubular 50 instead of into the sealing element 12. FIGS. 5 and 8 are slightly different. In FIG. 5 the end 60 of innermost ring 18 is manufactured with its end already bent so that in the set position that bent end 60 orients to the surrounding tubular 50 and bends end 62 toward the tubular 50 as shown in FIG. 8. Either the innermost ring 18 alone is bent at its end initially or more than one ring can have an initial end bend so that all but the outermost ring 14 are bent initially at a free end that contacts the surrounding tubular 50.

Those skilled in the art will appreciate that a backup ring assembly features multiple rings with circumferentially spaced slots to avoid extrusion paths also has a rotational locking feature to maintain relative orientations that preclude extrusion gaps from forming in the set position. The rings further have a capability of rotating in tandem with respect to the mandrel and of travelling axially relative to each other while still retained to the mandrel. The rings have different axial heights to allow the reduction or elimination of sharp ends facing the sealing element in the set position. The set position brings the ends of the rings closer to an alignment of their ends so that a blunt face is opposite the sealing element. The run in height differences also allow ends of inner rings to bend over ends of adjacent rings so that the sealing element sees a bent end of the innermost ring which is blunt. The ends of some of the rings other than the outermost can be bent for the run in position to encourage better end contact with the surrounding tubular as well as avoiding sharp ring ends from cutting into the sealing element. The ability of the rings to slide axially relatively to each other can be controlled with studs that force the rings toward a supporting mandrel. A bushing or bearing allows the assembly of all the rings to rotate in tandem relative to the mandrel to assure a better peripheral connection to the surrounding tubular to reduce or eliminate extrusion paths along the surrounding tubular wall.

The above description is illustrative of the preferred embodiment and many modifications may be made by those skilled in the art without departing from the invention whose scope is to be determined from the literal and equivalent scope of the claims below: 

We claim:
 1. An extrusion barrier assembly for a mandrel mounted sealing element in a borehole barrier, comprising: a plurality of nested discrete rings mounted to the mandrel for relative axial movement, with respect to the mandrel, of first ends of said rings nearest the mandrel when second ends of said rings are radially actuated from a run in position adjacent said mandrel to a set position in contact with a surrounding borehole wall.
 2. The assembly of claim 1, wherein: said rings comprise a plurality of axially oriented slots extending from a first axial end thereof, with said slots in adjacent rings circumferentially offset so as to avoid extrusion gaps in said set position.
 3. The assembly of claim 2, wherein: said rings are rotationally locked with respect to each other to maintain said circumferential offset of said slots.
 4. The assembly of claim 3, wherein: said rings are rotatably mounted to said mandrel.
 5. The assembly of claim 3, wherein: said rings each comprise at least one axial keyway such that keyways in said rings are aligned to accept a retainer that permits relative axial movement of said rings and precludes relative rotation between said rings.
 6. The assembly of claim 5, wherein: said keyways begin at a second axial end opposite said first axial end.
 7. The assembly of claim 3, wherein: said rings are retained to said mandrel with a retainer ring further comprising a lateral opening for advancing a force regulating retainer radially against said rings to regulate the force required to relatively move said rings in an axial direction.
 8. The assembly of claim 7, wherein: said rings each comprise at least one axial keyway such that keyways in said rings are aligned to accept a keyway retainer that permits relative axial movement of said rings and precludes relative rotation between said rings.
 9. The assembly of claim 3, wherein: said slots widen as between said run in and set positions while remaining circumferentially offset as between adjacent said rings.
 10. The assembly of claim 3, wherein: said rings vary in axial length in said run in position at said first axial end thereof.
 11. The assembly of claim 10, wherein: said rings comprise a longest in axial length innermost said ring and a shortest in axial. length outermost said ring to define an initial run in height difference, said height difference being reduced in said set position.
 12. The assembly of claim 10, wherein: said rings comprise a longest in axial length innermost said ring and a shortest in axial length outermost said ring to define an initial run in height difference, said height difference being eliminated in said set position.
 13. The assembly of claim 10, wherein: at least one of said rings at said first axial end thereof bends over a said first axial end of an adjacent ring when moved to said set position.
 14. The assembly of claim 10, wherein: at least one of said rings at said first axial end thereof is bent over a said first axial end of an adjacent ring in said run in position.
 15. An extrusion barrier assembly for a mandrel mounted sealing element in a borehole barrier, comprising: a plurality of nested discrete rings mounted to the mandrel having first ends of said rings nearest the mandrel and second ends, said second ends of said rings are radially actuated from a run in position adjacent said mandrel to a set position in contact with a surrounding borehole wall; said rings comprise a plurality of axially oriented slots extending from a first axial end thereof, with said slots in adjacent rings circumferentially offset so as to avoid extrusion gaps in said set position; said slots widen as between said run in and set positions while remaining circumferentially offset as between adjacent said rings; said rings vary in axial length in said run in position at said first axial end thereof.
 16. The assembly of claim 15, wherein: said rings comprise a longest in axial length innermost said ring and a shortest in axial length outermost said ring to define an initial run in height difference, said height difference being reduced in said set position.
 17. The assembly of claim 15, wherein: said rings comprise a longest in axial length innermost said ring and a shortest in axial length outermost said ring to define an initial run in height difference, said height difference being eliminated in said set position.
 18. The assembly of claim 15, wherein: at least one of said rings at said first axial end thereof bends over a said first axial end of an adjacent ring when moved to said set position.
 19. The assembly of claim 15, wherein: at least one of said rings at said first axial end thereof is bent over a said first axial end of an adjacent ring in said run in position.
 20. An extrusion barrier assembly for a mandrel mounted sealing element in a borehole barrier, comprising: a plurality of nested discrete rings mounted to the mandrel having first ends of said rings nearest the mandrel and second ends, said second ends of said rings are radially actuated from a run in position adjacent said mandrel to a set position in contact with a surrounding borehole wall; said rings comprise a plurality of axially oriented slots extending from a first axial end thereof, with said slots in adjacent rings circumferentially offset so as to avoid extrusion gaps in said set position; said slots widen as between said run in and set positions while remaining circumferentially offset as between adjacent said rings; said rings are rotationally locked with respect to each other to maintain said circumferential offset of said slots.
 21. The assembly of claim 20, wherein: said rings are rotatably mounted to said mandrel.
 22. The assembly of claim 20, wherein: said rings each comprise at least one axial keyway such that keyways in said rings are aligned to accept a retainer that permits relative axial movement of said rings and precludes relative rotation between said rings.
 23. The assembly of claim 22, wherein: said keyways begin at a second axial end opposite said first axial end.
 24. The assembly of claim 20, wherein: said rings are retained to said mandrel with a retainer ring further comprising a lateral opening for advancing a force regulating retainer radially against said rings to regulate the force required to relatively move said rings in an axial direction.
 25. The assembly of claim 24, wherein: said rings each comprise at least one axial keyway such that keyways in said rings are aligned to accept a keyway retainer that permits relative axial movement of said rings and precludes relative rotation between said rings.
 26. The assembly of claim 1, wherein: said rings are made from abutting or selectively attached segments.
 27. The assembly of claim 15, wherein: said rings are made from abutting or selectively attached segments.
 28. The assembly of claim 20, wherein: said rings are made from abutting or selectively attached segments. 